Surface Pro insomnia mode (lack of sleep) is driving me mad!

My Surface Pro (Windows 8.1 ProWMC RTM) has got a bad case of insomnia. No matter what I've tried adjusting, it absolutely will not sleep, hibernate, or whatever you want to call the state in which it saves what it's doing and restores it all when you turn it back on. Or maybe it does sleep but won't wake up properly.

Whether I tell it to sleep, or it times out on its own, the result when I next use it is as if I had done a hard power down. Any open files I didn't save are as if I never opened them, all changes lost. IE says my session ended abnormally. This is absolutely not how an 'instant-on' device is supposed to behave.

If anyone has no problems with sleep mode on 8.1, I beg you to please give me a detailed list of all the settings related to sleep and power management and tell me any workarounds you find helpful.